LIFK HISTORY OF DESM< )( INATHUS FUS( \. 



26 5 



similarly situated in the splanchnopleure (Fig. n, vbv), there 

 would seem to be no reason why they should not be considered 

 the homologues of a true vitelline circulation. 



The segmentation process results in the distribution of the 

 yolk granules to the cells of the blastula, and there early appears, 

 according to Hilton ('09), a differentiation of the cells into those 

 containing large and those containing small yolk granules, the 

 latter arranging themselves in a superficial layer surrounding 

 the former, which form the whole central portion of the mass. 

 Wilder ('04) found that the late blastula stage is reached in 



FIG. 5. Two embryos of Desmognathus fusca removed from two of the same 

 batch of eggs after 16 days of development, showing a difference in the rate of 

 development. Drawn with Abbe camera. X 9- 



about three days, w r hile Hilton reports the formation of the 

 yolk plug stage in about forty hours from the time the eggs are 

 laid. This discrepancy may, however, be due to an individual 

 difference in the rate of development, since Wilder found existing 

 simultaneously in the same batch of eggs, four-, eight-, and 

 sixteen-cell stages. 



By the eleventh day both the anterior and the posterior ends 

 of the embryo are well lifted above the surface of the yolk, and 

 the dorsal region of the body appears as a narrow welt or ridge 

 stretching between them. By the thirteenth or fourteenth day 



